Some so-called next generation sequencing methods, particularly single-molecule methods, sequence a target nucleic acid from a circular template. Template-directed incorporation of nucleotides by the circular template proceeds in circles generating multiple sequencing reads of the target nucleic acid. The multiple reads may contain different sequencing errors. Combination of multiple raw sequencing reads of the target nucleic acid generates a consensus sequence reducing the errors present in individual reads.
One type of circular template is formed by ligating hairpin loop adapters to the ends of a double-stranded target nucleic acid as in the Pacific Biosciences SMRTbell™ template. The single-stranded loop portions provide primer binding sites for extension through the target nucleic acid. A sequencing read generates alternating reads of hairpin loop segments and target nucleic acid encoded by the circular template. The reads of the target nucleic acid alternate between the sense and anti-sense strands.